A rotatable connector device which is mountable on a vehicle such as an automobile or the like includes a stator which is to be fixed mainly on the side of a vehicle body and a rotator which is to be assembled to the side of a steering wheel. The stator and the rotator are assembled together coaxially so as to be rotatable with respect to each other. In addition, a flat cable is accommodated in an accommodation space formed by the stator and the rotator such that the flat cable can follow the rotation of the steering wheel to be wound and rewound.
The flat cable electrically connects an electric device such as a horn module, an airbag module, an audio control module or the like equipped on the side of the steering wheel and a power supply on the side of the vehicle body to each other.
When such a rotatable connector device is assembled to the vehicle body or the steering wheel, the rotator occasionally rotates to cause the flat cable to be wound in a lopsided manner. When this occurs, the assembly may be performed in the state where the neutral position in a rotation direction of the steering wheel and the neutral position in the rotation direction of the rotatable connector device are shifted from each other. In the case where the rotatable connector device is assembled to the vehicle body in the state where the neutral position thereof in the rotation direction is not the neutral position in the rotation direction of the steering wheel, there is an undesirable possibility that when the steering wheel is rotated, the flat cable is ruptured.
Thus, a rotatable connector device, as described in Patent Document 1, including a relative rotation restriction unit for restricting relative rotation such that the rotator and the stator are not rotated with respect to each other until the steering wheel is completely assembled has been proposed.
The rotatable connector device described in Patent Document 1 operates as follows. A stopper, which is pushed up in an axial direction by the elasticity of a coil spring accommodated in a stator, is put into engagement with an opening of a rotator. This restricts the rotator and the stator 3 from rotating with respect to each other. When the stopper is pushed down by a cored bar of a steering wheel (corresponding to a steering device in Patent Document 1), the stopper is released from the opening. Patent Document 1 describes that the rotator and the stator are restricted from rotating with respect to each other, and are released from the restriction, by such a relative rotation restriction unit.
Today, meanwhile, a rotatable connector device is desired to be reduced in size because of constrains regarding an accommodation space on the side of the vehicle body.
However, the rotatable connector device including the relative rotation restriction unit as described in Patent Document 1 requires an accommodation space, for accommodating the coil spring, which has a height in the axial direction corresponding to a total sum of diameters of wire parts of the coil spring stacked in a contracted state, at least when the rotator and the stator are released from the restriction on the relative rotation.
In an attempt to solve this problem, Patent Document 2 disclosing a rotatable connector device shows, in figures, a rotation restriction unit using a coil spring having a hand drum shape as seen in a side view. Nonetheless, even though the hand drum-shaped coil spring is used so that the curved wire parts are stacked in a shifted manner when the coil spring is accommodated, in order to suppress the height thereof in the axial direction, it is difficult to significantly reduce the height of the accommodation space for the coil spring.
A rotatable connector device including the relative rotation restriction unit needs to allow for a stroke amount by which a stopper, for restricting the rotator and the stator from rotating with respect to each other and releasing the rotator and the stator from the restriction, moves in the axial direction. The stroke amount of the stopper needs to be set with a certain degree of margin in consideration of production variance and assembly variance. Owing to the margin, the stopper can restrict the rotator and the stator from rotating with respect to each other, and can release the rotator and the stator from the restriction, with certainty.
However, when the height of the rotatable connector device in the axial direction is reduced in order to fulfill the requirement of size reduction, the ratio of the height in the axial direction of the accommodation space for accommodating the contracted coil spring with respect to the height in the axial direction of the rotatable connector device is increased. Therefore, the stroke amount of the stopper cannot be set with a margin. When this occurs, the rotator and the stator may not be released from the restriction on the relative rotation with certainty.
As described above, the rotatable connector device including the relative rotation restriction unit using a coil spring has a problem of not sufficiently fulfilling the requirement of size reduction regarding the height in the axial direction.